Regardless of the particular approach, climate and energy observers say it’s encouraging to see so much gathering momentum at the state level, stressing that the measures provide crucial benefits beyond local boundaries.

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That said, it’s still difficult for state measures to add up to the impact of federal policies, particularly since the states pursuing carbon pricing already tend to be among the nation’s lowest emitters.

“You’re not tackling the dirtiest states,” says Danny Cullenward, an energy economist and lawyer at Near Zero, an environmental research think tank.

In addition, attacking the problem in a piecemeal fashion can create other complexities. Notably, carbon pricing policies can send companies or consumers into neighboring states to conduct their business, in what’s known as leakage. Indeed, the carbon tax proposals in Connecticut and Rhode Island are both contingent on neighboring states passing their own measures, out of fear that residents will cross a nearby border to, say, buy cheaper gas.

Any carbon pricing program also needs to be designed and implemented carefully to meet its goals. California’s cap-and-trade system “has not played a large role in driving emission reductions to date,” because the relatively loose cap allowed unused allowances to pile up, according to a recent Near Zero analysis. The same problem plagued the European Union’s pioneering emissions trading system, ultimately forcing an overhaul of the system earlier this year.

Still, the hope is that successful state programs will prompt other states and regions to follow their lead—perhaps someday even including the federal government.